For instance, let's suppose that we are in a room and we hear a person speaking in the hallway. If we start to speak at the same volume as that person do, would he hear us as loud as we hear him?
Mostly usually yes, in the same way that optical systems show the same attenuation in both directions.
but human mouths and ears are slightly directional and are slightly displaced, so tricks could be played using focusing structures to boost efficiency in one direction, eg: a speaking tube that leads from the mouth of one player to the ear of the other.
Also environment has an effect if it's more noisy in the hallway than in my room other player may not hear me.